Voltage transients may be produced in electrical circuits by a variety of things, such as lightning, AC power line induction or contact, electrostatic discharge or pulses generated by operation of electrical equipment. These phenomena can generate large currents on cables, telecommunications equipment, aircraft, and ships. Voltage transients can also penetrate and damage electrical systems, causing hardware damage or loss of stored data. Thus, voltage transients represent a threat to electrical/electronic equipment, especially in telecommunications equipment.
Various circuits and systems have been used for protecting telecommunications equipment from voltage transients. For example, circuits used with PBX out-of-building lines, special service lines such as carrier, pair-gain, and high speed data, and dedicated voice-band services such as pay phones and traffic-control communication lines have been designed to reduce damage caused by voltage transients. Conventional circuits utilize gas discharge tubes, transient voltage suppression thyristors, resistors, capacitors, inductors, avalanche diodes, and metal oxide varistors, to clamp transient voltages at prescribed potentials. These circuits may include a filter circuit comprising RC, RL or RLC circuits that are used to cutoff a prescribed range of frequencies. Sometimes the filtering is intentional, and sometimes it is not. Moreover, in order to have an effective filter circuit, the circuit designer must ensure that the resistance, capacitance and/or inductance values are maintained in a prescribed ratio. However, finding and maintaining a suitable "prescribed ratio" is no small task. In addition, the use of capacitors and inductors in a circuit or system can have a negative impact in terms of performance. For example, the saturation tendency of an inductor reduces its usefulness during impulse surges, especially at higher currents and slower risetimes. Nonetheless, conventional circuits have not considered eliminating capacitors, inductors and filtering from the overall design.
In light of the foregoing, there is a need for a system that protects telecommunications equipment from voltage transients as effectively as those heretofore developed, but which does not include capacitors, inductors and filtering.